The present invention relates generally to mixing and dispensing guns for use in the plastic foam industry, and more particularly, to a design of gun which is adapted for easy, low cost mass production manufacture and which is capable of performing the functions needed for precise mixing and dispensing of thermosetting chemical products resulting from the mixture of two reactive chemical components. Most particularly, the invention relates to a novel form of seal which is used and which is particularly effective in sealing a spool valve and the surrounding areas.
In recent years, there has been an ever increasing use of polyurethane and like plastic foams for a number of applications. Urethane and related products, including isocyanurates, silicones, phenolics, and epoxies, are well known as having a number of desirable characteristics. These include the potential for excellent heat insulation, compatibility with low cost blowing agents, reproducability of chemical characteristics and excellent chemical and physical properties in the finished product.
Many urethane foams are resistant to degradation by common solvents, moisture and atmospheric oxidation. Urethanes provide the best combination of heat insulation and physical strength for a given cost. The foam is a naturally adhesive material and bonds well to any number of substrates. In this connection, it can add structural strength to many article wherein such strength is an important element. Fire retardance may be achieved easily with available formulations.
Moreover, urethane foams, being the reaction product of two individual components, may be varied in chemical composition for a number of purposes. Thus, urethane foams may be formulated so as to provide a finished product which is quite rigid, which is semi-rigid, or which is somewhat flexible and/or elastomeric. Foams of the kind in question may be made with almost exclusively closed cells, or with a desired proportion of open cells.
The types of products with which the instant invention is concerned are primarily the closed cell foam types of product used for insulation purposes in building structures and open the celled product used for packaging applications. The components of the foam are passed at high pressures above 40-50 p.s.i. through a gun which serves to meter and mix the components thoroughly in a nozzle from which they are discharged. According to the invention, chemicals components are taken directly to a job site in pre-pressurized cylinders. The amount of product required to be dispensed is not so large as to require permanent, expensive equipment, as would be the case in a factory.
However, the amount of product used is significantly larger than could be accommodated by using small, individual aerosol cans, for example. The individual containers of the components carry from several pounds up to perhaps 25 to 50 or even more pounds or more of each component. These tanks are sufficiently portable to be moved about on the job site by one worker, but yet are able to provide sufficient foam to provide several hundred or even thousand board feet of coverage.
With the ability of the chemical supply tanks to be moved about, there has been a significant demand for a dispensing gun which would provide the advantages and characteristics of low cost, operating flexibility and reliability in use, and provide an excellent seal between the spool and the body of the gun.
One of these required characteristics is that the product be able to be mixed in a nozzle which can be used and then disposed of after use, and replaced with another nozzle at low cost for a succeeding job or succeeding phase of the job then being undertaken.
Another desirable characteristic is that the chemical products or constituents be able to be metered accurately and proportioned both as between themselves, and as a whole considering the desired dispensing rate.
A still further requirement of a gun of the type in question is that the valving be constructed and arranged so as to permit a proper proportioning action to be maintained even when the trigger is held completely opened or is opened within an intermediate range of positions to vary the discharge rate as desired.
An ideal gun, consequently, would be one which is able to be reliably manufactured at low cost and which will prevent premixing of the components, keeping them isolated from each other until they are discharged into the mixing chamber of an associated nozzle.
Another desirable characteristic of such a gun would be the ability to position a discharge nozzle correctly by "feel" and make it possible for the operator to insure himself that the nozzle is fully seated in a locked position before the gun is likely to be used.
Yet another desirable characteristic would be a gun having the porting designed so as not to have any dead space for the accumulation of the chemicals in the port where they may be exposed to the atmosphere. Specifically, where the isocyanate component of the polyurethane would be allowed to have contact with atmospheric moisture (humidity) and react and crystallize in the port, rendering the gun inoperable.
Accordingly, it is an object of the present invention to provide a gun which includes components which are easy to manufacture at low cost, incorporating a minimum number of components designed for mass production with no subcomponent assembly or remanufacture.
Another object of the invention is to provide a gun which includes a valve assembly adapted to insure that the components are not mixed with each other prior to their discharge into the mixing chamber of the associated nozzle.
Yet another object of the invention is to provide a valve arrangement which is adapted to promote mixing of the desired proportions of components at a variety of trigger or discharge rate settings.
Still another object of the invention is to provide a gun which is compatible with existing mixing and dispensing nozzles which are associated with the gun in use.
A further object of the invention is to provide a novel seal arrangement between the gun body and the spool valve.
A still further object of the invention is to provide a novel resilient arrangement to maintain sealing pressure on the area of the nozzle of the gun body wherein the seal is taking place.
An additional object of the invention is to provide an inlet passage for the gun wherein the nozzle end of the hose is equipped with a fitting which, by reason of being seated in the correct position, inherently insures that a correct amount of force is brought to bear on the sealing surface.
Another object of the invention is to provide a valve component seating arrangement which will allow for seating of the valve at high, low, and intermediate pressures.
Yet another object of the invention is to provide a combination load applying and slightly resilient member which may be used in the application sealing force.
The present invention achieves the foregoing and other objects and advantages of the invention by providing a gun body which includes a spool valve, an inlet and an outlet therefor, a slightly deflectable but unitary wall, and a combination load applying and wall deflecting component urged into position by the hose and having a set screw thereon, the combination being operative to apply a sufficient load to slightly deflect the wall of the housing surrounding the spool valve only in the area of compression by the wall deflecting component.
The manner in which these objects and advantages are achieved in practice will become more clearly apparent when taken in connection with a detailed description of the preferred embodiments of the invention set forth by way of example and shown in the accompanying drawings, in which like reference numbers indicate the corresponding parts throughout.